european college of sport science

Wednesday, June 24th, 2009
MRF RESPONSES IN THE ARM FLEXOR MUSCLES TO HIGH-FORCE ECCENTRIC EXERCISE
HANSSEN, K.E., PAULSEN, G., DRANGE, M., KADI, F., RAASTAD, T.
NORWEGIAN SCHOOL OF SCIENCES
Introduction: High-force eccentric exercise may result in muscle damage involving myofibrillar disruptions and in some cases segmental
fibre necrosis. The repair processes may involve activation of satellite cells leading to satellite cell proliferation and later differentiation
and fusion with other satellite cells or damaged myofibers. After activation, the proliferation and later differentiation of satellite cells are
driven by the myogenic regulatory factors (MRFs). Consequently, the expression of MRFs can be used as markers of myogenic events
during the course of activation of satellite cells (1). The purpose of this study was to investigate the MRF responses in the arm flexors after
unaccustomed eccentric exercise and to a repeated bout three weeks later. We hypothesized that in the exercised arm the MRF levels
would increase after bout 1, but after bout 2 the increase would be attenuated do to less damage in the repeated bout.
Methods: Thirty-three young males and females (23-28 years) participated. Seventy unilateral voluntary maximal eccentric actions with
the arm flexors were performed twice (bout 1 and 2) with the same arm, separated by three weeks. The participants were randomized
into a test and a control group. The exercise was performed with the same arm, randomly chosen, on bout 1 and 2. The other arm served
as a non-exercised control. Nine days after the exercise bouts, tests of the force-generation capacity were performed. Biopsies from m.
biceps brachii were collected from both exercised and control muscle 1, 48, 96, 168 hours after bout 1 and 1, 48 hours after bout 2. In
order to visualize satellite cells cross sections were analyzed for immunoreactivity against CD56/NCAM (immunohistochemistry- IHC), and
MRF protein content was determined using Western blotting.
Results:
The force-generating capacity measured as isometric torque was markedly reduced (-40-50%) after both exercise bouts. Long lasting
recovery indicates muscle damage confirmed by other histological methods. So far only three subjects have been analyzed for MRFs and
the preliminary results indicate that the MRF responses are according to our hypothesis. The rest of the samples will be analyzed the next
months and the complete results on MRFs and satellite cells will be presented at the congress.
Discussion: In this study, the combination of IHC and Western blotting will give new information about the MRF response after a single
bout of muscle damaging eccentric exercise and following a less damaging repeated bout of exercise.
References:
THE EFFECT ON NEUROMUSCULAR JUNCTION FORM AND CONTRACTILE PROPERTIES IN THE RAT SKELETAL MUSCLE
FOLLOWING THE ECCENTRIC CONTRACTION EXERCISE.
NISHIZAWA, T., YUKI, A., TAMAKI, H., KASUGA, N., TAKEKURA, H.
CHUKYO WOMEN’S UNIVERCITY JUNIOR　NATIONAL INSTITUTE OF FITNESS AND SPORTS, KANOYA, 　AICHI UNIVERSITY OF
EDUCATION
Introduction: The purpose of this study was to investigate the effect of the muscle damage by the exercise on neuromuscular junctions
(NMJs) form and function in the rat skeletal muscle. In skeletal muscle after eccentric contractions, exercise induced muscle injury has
been studied. Our studies so far have reported that significant changes in ultrastructural features of architecture of NMJs occurred in
skeletal muscle fibers damaged by BPVC during the degeneration processes. And degradation of the ultrastructural features in NMJs
occurred due to temporary denervation during muscle fiber degeneration processes. On the other hand, it is not clear the muscle damage
by exercise causes the abnormality of the neuromuscular junction. In this study, we observed the degeneration processes of NMJs
form following muscle fibers damages by eccentric contraction exercise. Additionally, the muscular contraction immediately after eccentric
contraction exercise was measured.
Materials and methods
Female Fischer 344/Jcl rats (10 weeks old, body weight, 150–170 g) were used. All procedures in the animal experiments were performed
in accordance with the guidelines presented in the Guiding Principles for the Care and Use of Animals in the Field of Physiological Sciences,
published by the Physiological Society of Japan.
Training protocol: Downhill training ran on the treadmill continuously for 5min running with 2min rest interval, 18bouts at 40m/min and 16
degree decline. Downhill training it carried out once.
Contraction characteristic: Single muscle fibers were dissected from the extensor digitorum longus (EDL) muscles. Muscle contraction
characteristic was measured after eccentric contraction exercise: 1,2,4,8,16,24,60 hours after exercise. The contraction characteristic
developed by the nerve stimulation and by the muscle stimulation.
Morphological observation: We observed the degeneration of neuromuscular junctions on the muscle after eccentric-exercise:
1,2,4,8,16,24,60 hours after exercise. Three Types of fibers were classified based on differences ATPase activity. The muscle fiber composition
is shown at muscle fiber for different types the number ratio. The morphological observation of neuromuscular junction by optical
microscope used cholinesterase and silver staining.
Results: Significant changes in NMJs form occurred in skeletal muscle fibers damaged by eccentric contraction exercise. There was a
difference in comparing indirect stimulation tension for the direct stimulation tension after exercise 4 hours. Significant changes was
recognized after 16 hours. Significant changes Significant changes of both characteristics appeared after 16 hours. The muscle contraction
characteristic was decreased, when the NMJs form is abnormal. It was indicated that the abnormal NMJs form was a factor of the
decrease of the muscle contraction force.
EFFECTS OF TENDON VIBRATION ON DISCHARGE BEHAVIOR OF HUMAN MOTOR UNIT DURING SUBMAXIMAL ISO-
METRIC CONTRACTION
KAMO, M.
JAPAN WOMEN'S COLLEGE OF PHYSICAL EDUCATION
Introduction　
Discharges of motor units (MU) are well known to show elongating trends in the spike interval during voluntary constant-force isometric
contraction (e.g. Kamo, 2002), but neural mechanisms underlying those trends remain unclear. A reduction in Ia afferent activity have
been advanced as a possible cause the spike interval elongation (Macefield et al., 1991; Griffin et al., 2001). This study examined effects of
manipulation of peripheral afferent by tendon vibration on elongating trends in spike interval of MU during the constant-force contraction.
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